I think it has more to do with where the airport has room for the large xray machines than whether it's better for the TSA to inspect with or without the passenger present. At DFW the inspection was initially done near the check-in counter. The passenger had to get the bag tagged and then haul it over to the TSA setup. Nowadays, presumably after some remodeling, the TSA has moved downstairs and bags go on the conveyer, just like always.

I have a big collection of TSA notices. I like to fly around with my S&S coupled bicycle (google it) to ride in various places around the US and Europe. It's an unusual enough setup they open it nearly every time and then have to go find me to help repack and close the case. I've gotten accustomed to it.